An audio interface (such as a headphone socket) of an existing audio signal sending apparatus (such as a mobile communication terminal) and an audio interface of an audio signal receiving apparatus (such as a headphone) generally use a four-section interface, in which a pin 1 and a pin 2 are audio pins, i.e., a left-channel pin and a right-channel pin respectively. However, a pin 3 and a pin 4 of different types of audio interfaces play different roles, that is, there are two types of audio interfaces: the pin 3 is a MIC pin (a microphone pin) and the pin 4 is a GND pin (a ground pin); the pin 3 is a GND pin and the pin 4 is a MIC pin.
As different types of audio interfaces exist, when the audio interface of the audio signal sending apparatus (such as the mobile communication terminal) and the audio interface of the audio signal receiving apparatus (such as the headphone, a headset) do not match, the audio signal sending apparatus can neither communicate with the audio signal receiving apparatus via the MIC pin of the audio interface, nor transmit an audio signal to the audio signal receiving apparatus via the audio pins (i.e., the left-channel pin and the right-channel pin) of the audio interface normally.